Tub boxes are commonly used to form a cavity in a concrete slab for receiving a trap for a bath tub or the like so the tub can easily be connected to the drain system. Typically such tub boxes comprise two identical plastic housing portions fitted together, each including continuous side walls forming a hollow enclosure open at one end and closed at the other end. Surrounding the open end of each housing portion is a radially outwardly protruding edge flange adapted to be placed in mating engagement with the edge flange of another housing portion to form a joint therebetween.
Suitable round knockouts are provided in one or more side walls, and if desired, in the closed end wall of each housing portion. When removed, these knockouts provide one or more round access openings for passage of a pipe used to connect the trap within the tub box to the drain system. Also, it is generally known to extend the knockouts in the side walls all the way to the open end of each housing portion so that when one of the knockouts is removed, the plumber can locate the pipe in the resulting knockout opening without having to insert the end of the pipe through the knockout opening.
In some installations the plumber may want a round knockout opening in a side wall of the tub box in order to provide a close fit with a round pipe extending through the opening, whereas in other installations the plumber may want the convenience of having the knockout opening extend all the way to the open end of the housing portion to eliminate having to insert the end of the pipe through the opening. This has the drawback that the same tub box could not be used for both applications.
Another drawback of previous tub boxes is that the joint that is formed between the engaging edge flanges of two housing portions is not always effective in keeping concrete or dirt that is placed around the tub box after installation from entering the tub box between the flange portions.
Moreover, when adhesive is used to bond the edge flanges of the housing portions together to secure the trap cavity within the box from concrete, rodents and vermin, it is sometimes difficult to keep a bead of adhesive in place on the edge flanges of the housing portions before the edge flanges are pressed into engagement with each other.
Further, it is somewhat difficult to cut off the top portions of previous tub boxes that protrude above the concrete slab. Also, there is a risk that if the top portions of the tub boxes are inadvertently kicked or hit before they are cut off, they might break off with a jagged break and have to be dug out and replaced.
Another disadvantage of previous tub boxes is that the housing portions sometimes stick together when stacked during storage and shipping, making it difficult to pull them apart when desired.